Greenhouse gases (GHGs) are carbon-containing compounds that absorb and hold heat in the atmosphere, preventing it from escaping to space. The levels of many of these gases are at their highest ever recorded, largely due to human activities such as the burning of fossil fuels. These changes in greenhouse gas levels cause global warming, with the result that Earth’s temperature is rising. This is bad for the health and well-being of people, and also negatively affects natural and human-built environments, and our food supply.

There are both natural and human-caused GHGs, with carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and fluorinated gases such as chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs) and sulphur hexafluoride (SF6) accounting for most of the human-caused emissions. The natural sources of methane are wetlands, tundra and ocean bottom sediments; significant human-caused methane sources include landfills, livestock farming (especially enteric fermentation), rice agriculture, bioenergy, fossil fuel combustion and coal mining.

Across Europe, the manufacturing sector is one of the largest emitters of GHGs, mostly due to the combustion of fossil fuels. Other industries such as transport and energy generation (including electricity production) also contribute.

The relative impact of each of the individual greenhouse gases on global temperatures is defined by their Global Warming Potential (GWP) – a measure of how much they warm the planet when released into the atmosphere. A higher GWP indicates that the gas has a greater effect per unit of emission. The atmospheric lifetime of the gas is also taken into account, as is its radiative properties and the availability of sinks that remove it from the atmosphere.